From BlenderWiki

Open/Free Blender Publications

This section of the Blender wiki lists some of the Open/Freely available publications available for Blender, giving a brief and general description of each of them and information on how get access them.

The 2.5x release of Blender has meant a large change in the way Blender works and in the way its interface is displayed. This means that publications written for a version of Blender which are earlier than 2.5x will often be very different than those written for Blender versions after 2.5.

With this in mind this list of books is split into those before 2.5 and those after 2.5.